If you receive an "Invalid Serial Number" error during registration, it's possible the serial number is not correct, but this error can also be caused by a permissions issue.
If you are working on a PC, please make sure that you are logged on as the administrator.
If you are on a MAC, you will need to run the Repair Permissions utility, to do so:
1 - Go to Applications > Utilities, and launch the Disk Utility program
2 - In the left hand panel of the utility, single click the hard drive icon to highlight it
3 - Click the First Aid tab
4 - Click the Verify Disk Permissions button
This will take a couple of minutes to run. When complete launch and register the Optix software.